Ex-judge Robert Fisher says it was ex-judge Ian Binnie's conclusion David Bain was "factually innocent" and recommendation of compensation which overstepped his mark.
The retired Canadian judge is criticised by Mr Fisher and justice minister Judith Collins "for going beyond his mandate."
Mr Fisher was brought in to undertake a peer review of Mr Binnie's report after Miss Collins slammed it, saying it appeared to contain assumptions based on incorrect facts and showed a misunderstanding of New Zealand law.
She said it also "lacked a robustness of reasoning used to justify its conclusions".
Mr Binnie's mandate was spelt out in a letter from then-justice minister Simon Power, dated November 10, 2011.
Mr Power wanted to know:
- Whether you are satisfied that Mr Bain is innocent on the balance of probabilities and, if so, whether he is also innocent beyond reasonable doubt.
- Any factors particular to Mr Bain's case (apart from your assessment of innocence beyond reasonable doubt) that you consider are relevant to cabinet's assessment of whether there are extraordinary circumstances such that it is in the interests of justice to consider his claim.
"Because the question of whether 'extraordinary circumstances' apply in a particular case is ultimately a judgment for the cabinet to make I am seeking advice on factors you consider relevant to the assessment rather than an opinion on whether Mr Bain's application qualifies for the exercise of the residual discretion reserved by Cabinet," Mr Power wrote.
In his peer review, Mr Fisher said Mr Binnie overlooked these instructions and defined his own mandate as follows:
"In short, my mandate is to express an opinion about whether or not:
David Bain is factually innocent of the five killings and, if so,
Whether the circumstances of his conviction were so extraordinary as to warrant an ex gratia payment of compensation by the New Zealand government.
It is important to emphasise, as the minister's letter makes clear, that my role is to provide a recommendation not a decision. The question of David Bain's compensation rests firmly in the hands of the cabinet.
"Binnie J was not asked to make a recommendation. He was asked to advise whether he was satisfied David Bain was innocent, on either the balance of probabilities or beyond reasonable doubt," Mr Fisher wrote.
He said Mr Binnie was effectively told his opinion on the way in which discretion should be exercised was not warranted or needed.
But Mr Binnie did make his opinion clear, saying he believed it was more likely than not that Mr Bain is "factually innocent" and that he should receive compensation for the wrongful conviction of the 1995 murders.
"It is my opinion that the egregious errors of the Dunedin police that led directly to the wrongful conviction make it in the interest of justice that compensation be paid," according to Mr Binnie.
On the other hand, Mr Fisher said by giving the unsolicited conclusions, Mr Binnie encroached on matters which should have been left for cabinet to decide.
"It must immediately be said that Binnie J would not have been responsible for the publicity that followed. However, the problem of going beyond his mandate has been compounded by the publicity given to opinions which were intended to remain confidential unless and until cabinet elected to release them."
Mr Fisher said Mr Binnie exceeded his jurisdiction and by doing so, could have opened up his report to judicial review.
When Mr Power initially wrote to Mr Binnie, he told him there was no legal right to compensation in New Zealand for wrongful conviction or imprisonment but the government could decide to pay compensation on an ex-gratia basis.
Mr Binnie and Mr Power agreed to an hourly rate for the retired judge of $NZ450.
Mr Binnie carried out a number of interviews for his report, including talking to retired police officers and Mr Bain himself.
In his interview, Mr Bain talked of the loss earnings and future opportunities after spending 13 years in prison.
He said he had been told he had the potential to have an opera singing career as successful as Jonathan Lemalu.
"Mr Lemalu is now engaged two years in advance and is singing all over the world. In 1992, my singing teacher told me when I started lessons that I had a wonderful voice and that I could one day create a valuable career for myself."
He said since his arrest he had not taken part in any form of music and the life he was planning has gone out the window.
"I feel as though I lost the major earning years of my life. I have not been able to advance my life. I have only lived through the goodwill of others."